Electric vehicles include a battery for powering an electric drive system. The battery can include multiple battery cells that are rechargeable by a DC voltage. For plug-in electric vehicles, the local electrical grid is used for recharging the battery when the vehicle is not being driven. Because most electrical grids provide a three-phase AC voltage, however, power from the local electrical grid must first be converted into a suitable DC voltage.
A variety of circuits exist for converting a three-phase AC voltage into a DC voltage. One known circuit is illustrated in FIG. 1 and includes a first stage converter and a second stage converter. The first stage converter receives a DC voltage from a front end rectifier (not shown) and outputs to a DC link capacitor, while the second stage converter provides galvanic isolation for the circuit. The first stage converter in this circuit is a dual-active-bridge (DAB) converter. In operation, its DC input is inverted by a primary-side bridge and rectified by a secondary-side bridge. The DAB converter is typically operated by a controller to regulate the magnitude of the DC output in accordance with battery charging requirements.
In some applications, it is desirable to implement a single stage design. In practice however local electrical grids can provide an unbalanced three-phase AC voltage. If not corrected, an unbalanced voltage can cause voltage distortions or current ripple in the DC output, which may be harmful to the battery during recharging. Existing single stage designs however are poorly suited for applications in which the local electrical grid is unbalanced. Accordingly, there remains a continued need for an improved single stage control circuit for recharging vehicle batteries, and in particular, a single stage control circuit including a DAB converter.